High-intensity laser systems offer completely new opportunities to nonlinear optics, which – just like other effects induced by these lasers – are dominated by relativistic electrodynamics. From the very beginning, nonlinear optics’ preeminent application was the generation of light with frequencies different from the irradiated one. In nonlinear optics at high-intensity lasers, spotlight is put on frequency conversion into the extreme UV or even X-ray range.

The interaction of high-intensity laser radiation and matter actually opens up a whole set of approaches to generating short-wavelength radiation with various properties. Generation of higher harmonics on surfaces leads, for example, to coherent XUV radiation, while Thomson scattering on high-energy electrons is capable of producing X-ray radiation. A common characteristic of these radiation sources is their comparatively high conversion efficiency. Furthermore, these high-frequency radiation sources distinguish themselves by their extremely short pulse duration, which on the one hand enables high temporal resolution in applications, on the other hand leads to high intensities.

Apart from fundamental issues, this research is governed by the multitude of possible applications. Within HI Jena, the following aspects are predominant:

Precision spectroscopy in the XUV and X-ray spectral range is dependent upon spectrometer development in the same way as it is upon radiation source development.

High-intensity XUV and X-ray sources may be used to induce and investigate nonlinear, correlated multi-electron ionization.

Performance of X-ray free electron lasers could be improved considerably if a sufficiently intense, coherent X-ray source was available.